Indian Prime Minister Manmohan Singh, left, smiles as he presents "Padma Shri" award to Noboru Kawashima, an honorary professor of Tokyo University during his lecture in Tokyo, Tuesday, May 28, 2013. Padma Shri is one of India's awards for civilians to recognize their distinguished contribution in various fields. (AP Photo/Koji Sasahara)

India's Prime Minister Manmohan Singh makes a speech during a luncheon hosted by the business lobby Keidanren, the Japan Chamber of Commerce and Industry (JCCI) and the Japan-India Business Co-operation Committee in Tokyo, Japan, on Tuesday, May 28, 2013. Singh arrived in Japan Monday for a four-day official visit. (AP Photo/Tomohiro Ohsumi, Pool)

India's Prime Minister Manmohan Singh, left, poses with Hiromasa Yonekura, chairman of Sumitomo Chemical Co. and chairman of the business lobby Keidanren, during a luncheon hosted by Keidanren, the Japan Chamber of Commerce and Industry (JCCI) and the Japan-India Business Co-operation Committee in Tokyo on Tuesday, May 28, 2013. Singh arrived in Japan Monday for a four-day official visit. (AP Photo/Tomohiro Ohsumi, Pool)

India's Prime Minister Manmohan Singh, left, and Hiromasa Yonekura, right, chairman of Sumitomo Chemical Co. and chairman of the business lobby Keidanren, make a toast during a luncheon hosted by Keidanren, the Japan Chamber of Commerce and Industry (JCCI) and the Japan-India Business Co-operation Committee in Tokyo on Tuesday, May 28, 2013. Singh arrived in Japan Monday for a four-day official visit. (AP Photo/Tomohiro Ohsumi, Pool)

Ensuring that sea lanes remain open and free is vital for the region's prosperity, given its dependence on oil imports from the Middle East, Singh said on a four-day Japan visit focused on firming up the two countries' economic ties and other cooperation.

"India's relations with Japan are important not only for our economic development but also because we see Japan as a natural and indispensable partner in our quest for stability and peace in this vast region," Singh said in a speech.

India has sought to cultivate closer ties with Japan and other Asian countries, while upgrading its military capabilities, partly in response to a perceived challenge from China and also from neighboring Pakistan. Both India and Japan have long expressed concern over potential threats to their energy supplies due to sea lanes vulnerable to piracy and blockades.

The business newspaper Nihon Keizai Shimbun reported that Tokyo and New Delhi were close to reaching agreement on the sale of Japanese-made amphibious aircraft to India.

Just days ago, Chinese President Xi Jinping met Singh in India, and the world's two most populous nations pledged to work together for regional stability and economic growth, despite rising friction between the two Asian giants.

Singh made no direct mention of China, though he emphasized India and Japan's "shared commitment to the ideals of democracy, peace and freedom."

"We have shared interests in maritime security, face similar challenges to our energy securities. There are strong synergies between our economies, which need an open, rule-based international trading system to prosper," he said.

Among other priorities, Japan and India are working toward a deal on nuclear energy cooperation, as Tokyo tries to boost exports of atomic technology and other infrastructure to help revive the economy.

Prime Minister Shinzo Abe is eager to promote sales of Japanese nuclear technology as part of Japan's push to expand exports, especially in emerging markets in Asia and the Middle East that offer stronger growth potential than at home, without the political tensions that plague Tokyo's dealings with mainland China.

Earlier this month, Japan and India signed agreements on economic cooperation and investment, including multibillion-dollar plans for industrial corridors between New Delhi and Mumbai, and between Chennai and Bangalore. The two sides are also expected to discuss closer military ties.

Despite both sides' hopes for closer ties, trade between Japan and India has not yet taken off. Japan's exports to India fell nearly 5 percent in the fiscal year that ended in March to 842.1 billion yen ($8.25 billion) — one-thirteenth of the amount Japan shipped to China. Imports rose 4.5 percent from a year earlier to 579.1 billion yen ($5.7 billion), according to Japanese figures.